Generally, an ink-jetting recording apparatus, which is an example of liquid ejecting apparatus, includes a recording head having a nozzle, an ink-jetting means for ejecting ink from the nozzles (for example, a piezoelectric vibrating member or a heat-generating member), and a main controlling part that controls the ink-jetting means based on recording data.
The nozzle of the recording head may be clogged with thickened ink. In order to prevent clogging of the nozzle with the thickened ink, the thickened ink may be forcibly sucked from the nozzle.
Tube pumps are commonly used for forcibly sucking the thickened ink. In a tube pump, a tube is collapsed by a pulley, and then returns to an original shape of the tube due to rigidity thereof. The latter volume change provides a suction power.
However, the rigidity of the tube may change depending on temperature change or the like, so that suction speed may also change undesirably. In addition, in order to increase a volume of sucked ink, it is effective to raise a rotation speed of the pulley. However, there is no effect if the pulley is rotated at a speed faster than that at which the collapsed tube returns to the original shape. That is, the volume of sucked ink can not be increased greatly. In addition, if the diameter of the tune is increased, the volume of sucked ink may be increased. However, in that case, the thickness of the tube has to be increased in order to maintain the rigidity of the tube, which results in the larger sucking system.
The inventor has paid attention to a built-in slide-rotator type of positive displacement pump, because it is easy to downsize and optimally design the built-in slide-rotator type of positive displacement pump depending on a driving rotational speed and/or a required flow rate.
However, in the built-in slide-rotator type of positive displacement pump, there is the following problem, that is, when the inside of the positive displacement pump comes to nearly a dry state due to a long disuse or the like, the seal tightness between the pump frame (casing) and the slide-rotator (gear or the like) may be weakened so that the suction power may be considerably reduced.
JP Laid-Open Publication No. 55-64178 discloses a technique wherein a wetting agent is injected from outside into between a seal ring and a seal plate before driving a gear pump (an example of built-in slide-rotator type of positive displacement pump), when a kind of heated liquid is conveyed by the gear pump.
However, it is necessary to inject the wetting agent into the built-in slide-rotator type of positive displacement pump only when the inside comes to nearly a dry state. That is, if the wetting agent is injected in the built-in slide-rotator type of positive displacement pump always before driving the positive displacement pump, the wetting agent may be wasted in surplus. This is not preferable.